Tenofovir disoproxil fumarate is a prescription antiviral tablet. Its active ingredient is Tenofovir disoproxil fumarate, also called tenofovir DF or TDF. It belongs to a group of HIV medicines called nucleotide reverse transcriptase inhibitors. It is used to treat two long-term viral infections: HIV-1, where it is always taken together with other HIV medicines, and chronic hepatitis B, a long-term infection of the liver. Tenofovir-containing medicines are also prescribed to prevent HIV in people at high risk, an approach called pre-exposure prophylaxis, or PrEP. It lowers the amount of virus in the body but does not remove the virus, so treatment is usually long term.

Tenofovir disoproxil fumarate is a tablet taken by mouth once a day. The body changes the medicine into its active form, tenofovir, inside the cells. Tenofovir blocks two viral enzymes: reverse transcriptase, which HIV uses to copy itself, and the hepatitis B polymerase, which the hepatitis B virus needs to copy its DNA. With these enzymes blocked, the viruses cannot multiply as fast, so the amount of virus in the blood falls.

In HIV care, Tenofovir disoproxil fumarate is one part of a combination of medicines. It is never used on its own for HIV, because the virus quickly becomes resistant when a single medicine is used alone. In chronic hepatitis B, the World Health Organization recommends tenofovir as a preferred first-line antiviral, because it works well and resistance to it develops slowly. Hepatitis B treatment is usually long term, and many people continue it for years.

The medicine comes as 300 mg tablets, which contain the same amount of active ingredient as the 245 mg tablets sold in the European Union. Lower-strength tablets and an oral powder are made for children. It can be taken with or without food.

Tenofovir disoproxil fumarate needs medical supervision. The US label carries two boxed warnings, the strongest type of warning a medicine can have. The first is a rare but serious build-up of acid in the blood called lactic acidosis, together with an enlarged, fatty liver. The second is a flare of hepatitis B that can happen when treatment is stopped. The medicine can also harm the kidneys and lower bone mineral density, so kidney and liver blood tests are done before treatment starts and during treatment. Tell your doctor about every other medicine you take, especially painkillers such as ibuprofen and naproxen, because some medicines add to the strain on the kidneys. Do not stop this medicine on your own.

• Active ingredient: Tenofovir disoproxil fumarate. Each 300 mg tablet contains 300 mg of Tenofovir disoproxil fumarate, which is equal to 245 mg of tenofovir disoproxil.
• Other tablet strengths (US labelling): 150 mg, 200 mg and 250 mg tablets are made for children, and an oral powder is available for children who cannot swallow tablets.
• EU versions: the same tablets are labelled as 245 mg in the European Union; that strength is for adults and adolescents 12 to under 18 years. Lower-strength 123 mg, 163 mg and 204 mg tablets are made for children 6 to under 12 years, chosen by weight band, and 33 mg/g granules are available for children from 2 to under 18 years.
• Inactive ingredients in the tablets: croscarmellose sodium, lactose monohydrate, magnesium stearate, microcrystalline cellulose and pregelatinised starch. The film coating of the 300 mg tablet contains hypromellose, lactose monohydrate, titanium dioxide and triacetin. Tell your doctor if you cannot have lactose, because the tablets contain a type of sugar from milk.

Tenofovir disoproxil fumarate is used for:

• HIV-1 infection: in adults and in children from 2 years of age, always together with other HIV medicines.
• Chronic hepatitis B: in adults, and in children from 12 years of age according to the US label. The World Health Organization recommends tenofovir as a preferred first-line antiviral for this infection.
• Preventing HIV in people at high risk (PrEP): the World Health Organization recommends oral PrEP that contains Tenofovir disoproxil fumarate for people at substantial risk of HIV infection. PrEP is started and monitored by a doctor.
• Lowering the chance of hepatitis B passing from mother to baby: the World Health Organization recommends antiviral treatment in pregnancy for women with hepatitis B, to reduce the risk of passing the virus to the baby.

1. Treats two long-term viral infections: Tenofovir disoproxil fumarate works against both HIV-1 and the hepatitis B virus, so one medicine covers two infections in people who have both.
2. A simple once-daily routine: it is taken once in 24 hours, and it can be taken with or without food.
3. A preferred hepatitis B treatment: the World Health Organization recommends tenofovir among the preferred first-line antivirals for chronic hepatitis B, because resistance to it develops slowly.
4. A backbone of HIV treatment: it is widely used with other HIV medicines, and the combination keeps the virus suppressed.
5. Proven for HIV prevention when prescribed: the World Health Organization recommends tenofovir-based oral PrEP for people at substantial risk of HIV.
6. Options for children: lower-strength tablets and an oral powder let children take the medicine in a form they can manage.
7. Risks that can be checked: the main long-term concerns, kidney and bone effects, are looked for with regular blood tests, so problems can be found early.

Common Side Effects (Usually Mild and may lessen with continued use)

• Feeling sick (nausea) or being sick (vomiting)
• Diarrhoea
• Headache
• Dizziness
• Feeling weak or very tired
• Rash or itching
• Stomach pain, bloating or wind
• Trouble sleeping, or low mood
• Fever
• Low phosphate levels, seen on a blood test
• Raised liver enzymes, seen on a blood test
• A small fall in bone mineral density, seen on a bone scan

Serious Side Effects (Seek Urgent Medical Attention)

• Lactic acidosis: a rare build-up of acid in the blood that can be fatal. Signs include fast, deep breathing, feeling very drowsy, and feeling sick with stomach pain.
• Severe liver problem with fat build-up (hepatomegaly with steatosis): an enlarged liver with extra fat inside it. Signs include pain in the upper right side of the tummy, feeling very tired, and yellowing of the skin or eyes.
• Kidney problems, including acute kidney injury and Fanconi syndrome: Fanconi syndrome is a rare condition in which the tiny tubes inside the kidneys stop holding on to minerals and nutrients the body needs. Signs include passing much more urine than usual, being very thirsty, tiredness, bone pain and muscle weakness. A small number of people have developed kidney failure.
• Bone softening (osteomalacia) and bone loss: ongoing or worsening bone pain, or bones that break more easily, needs medical attention.
• Inflammation of the pancreas (pancreatitis): severe stomach pain that spreads to the back, with nausea and vomiting.
• Immune reconstitution syndrome: as the immune system recovers, it may start fighting infections that were already in the body, or turn on the body's own tissues. This can cause new or worsening symptoms, sometimes several months after treatment starts.
• Hepatitis B flare after stopping: if you have hepatitis B and stop treatment, the infection can flare up suddenly and seriously. This is why the label carries a boxed warning about stopping.
• Muscle breakdown (rhabdomyolysis): severe muscle pain or weakness with dark, cola-coloured urine.
• Nephrogenic diabetes insipidus: a rare kidney problem in which large amounts of dilute urine are passed and the person feels constantly thirsty.

• Take Tenofovir disoproxil fumarate exactly as your doctor prescribes, once a day.
• Swallow the tablet whole with a glass of plain water. Do not crush, chew or break it.
• The US label says it can be taken with or without food. Keep to one routine each day, so the amount of medicine in your body stays steady.
• Take it at the same time every day. A phone alarm or a weekly pill box can help you remember.
• If your child takes the oral powder, mix it with soft food such as applesauce, baby food or yoghurt, stir it well and let your child eat it straight away. Do not mix the powder with liquid.
• Keep taking it even when you feel well. Missing doses gives the virus a chance to become resistant, and in hepatitis B it can also lead to a flare.
• Do not let your supply run out. Ask for a refill well before the last tablet.
• Do not stop or pause treatment without talking to your doctor first.

Tenofovir disoproxil fumarate is a prodrug. A prodrug is a medicine that is not active when it is swallowed; the body has to change it into the active form. Here, the body strips away part of the molecule and leaves tenofovir, which then has two phosphate groups added inside the cells. The finished product is called tenofovir diphosphate, and this is the form that fights the viruses.

Tenofovir diphosphate is an acyclic nucleoside phosphonate. In plain words, it is a small, flexible molecule built to look like adenosine, one of the four building blocks that viruses use to copy their genetic material. When HIV reverse transcriptase or the hepatitis B polymerase tries to copy the virus and picks up tenofovir diphosphate by mistake, the new chain of DNA cannot grow any further. This is known as chain termination.

Reverse transcriptase is the enzyme HIV uses to turn its RNA into DNA, a step it must complete before it can settle into a human cell. The hepatitis B polymerase does a similar job for the hepatitis B virus. Blocking these enzymes slows both viruses down, which is why the amount of virus in the blood falls and why the immune system gets a chance to recover.

Because the target is a viral enzyme and not a human one, the medicine does not kill cells directly. It also stays inside cells for a long time, so one tablet a day keeps working around the clock.

• Take your tablet at the same time every day. A phone alarm makes this easier.
• Swallow it whole with plain water. Do not crush or chew it.
• Keep at least a month of tablets at home, so you never run out.
• Never stop on your own, even if you feel completely well. In hepatitis B, stopping can cause a serious flare.
• Keep your blood test appointments. They check your kidneys, your liver and your phosphate levels.
• Ask your doctor or pharmacist before using painkillers such as ibuprofen, naproxen or high-dose aspirin.
• Tell every doctor, dentist and pharmacist that you take Tenofovir disoproxil fumarate.
• If you feel dizzy, do not drive or use machines until you feel normal again.
• Store the tablets in the original bottle with the lid tightly closed.
• Do not share your medicine with anyone else, even someone with the same infection.

• Store the tablets at 25°C (77°F). Short trips between 15°C and 30°C (59°F and 86°F) are allowed, which is ordinary room temperature.
• Keep the bottle tightly closed, and leave the desiccant sachet inside the bottle to protect the tablets from moisture.
• Keep the tablets in the original container they came in.
• Keep them out of the sight and reach of children. The bottle has a child-resistant cap.
• Do not store them in the bathroom or next to a sink, and keep them away from heat.
• Do not use the tablets if the seal over the bottle opening is broken or missing.
• Do not flush unwanted tablets down the toilet. Ask your pharmacist about a medicine take-back scheme so that children and pets cannot reach them.

• Meals: the US prescribing information says Tenofovir disoproxil fumarate can be taken with or without food. No particular meal is required.
• Same routine: taking the tablet at the same time each day keeps the amount of medicine in your body steady, and that matters more than the food itself.
• No food restrictions: the prescribing information does not list any food, fruit juice or dairy product that must be avoided with this medicine.
• Alcohol: alcohol is not listed as an interaction, but heavy drinking can harm the liver, which matters most if you have hepatitis B.
• Herbal products: MedlinePlus advises talking to your doctor before using St John's wort with this medicine.

• Didanosine: Tenofovir disoproxil fumarate raises the level of didanosine in the body, which increases the risk of pancreatitis and nerve damage. The label says the didanosine dose should be reduced, and that it should be stopped if reactions appear.
• Atazanavir: tenofovir lowers the level of atazanavir. The label says atazanavir must be given with ritonavir when it is used with this medicine.
• Ritonavir-boosted protease inhibitors (lopinavir, atazanavir, darunavir): these raise the level of tenofovir in the body. People taking them are monitored for tenofovir side effects.
• Hepatitis C antivirals (ledipasvir with sofosbuvir, sofosbuvir with velpatasvir): these raise the level of tenofovir. Doctors monitor for tenofovir side effects and may choose a different hepatitis C medicine.
• Adefovir: the label says Tenofovir disoproxil fumarate should not be combined with adefovir, another hepatitis B antiviral.
• Other tenofovir products: do not take Tenofovir disoproxil fumarate together with any other medicine that contains tenofovir.
• Medicines that affect the kidneys: acyclovir, cidofovir, ganciclovir, valacyclovir, valganciclovir, aminoglycoside antibiotics such as gentamicin, and high-dose or repeated painkillers such as ibuprofen and naproxen. These can raise tenofovir levels or add to the strain on the kidneys.
• Medicines with no important interaction: the label lists no significant interaction with efavirenz, methadone, nelfinavir, oral contraceptives, ribavirin or sofosbuvir.
• St John's wort: MedlinePlus advises talking to your doctor before using it.

• Kidney disease: if creatinine clearance is below 50 mL/min, or if you are on dialysis, the dosing schedule is changed. Kidney function is checked before and during treatment.
• Hepatitis B: stopping treatment can cause a serious flare. Liver blood tests are checked for several months after treatment ends. People with hepatitis B are also offered an HIV test before starting, because HIV changes how the liver infection is managed.
• HIV: Tenofovir disoproxil fumarate must not be used alone for HIV. Using a single HIV medicine lets the virus become resistant, which makes later treatment harder.
• Bone disease: tell your doctor if you have osteoporosis, a previous fracture or other bone problems. The label says a bone density scan may be considered, and bone loss and bone softening have been reported with this medicine.
• Liver disease: rare cases of lactic acidosis with an enlarged, fatty liver have happened. The label advises extra caution in people who have risk factors for liver disease, although these reactions have also happened in people without them. Liver function is monitored during treatment.
• Lactose intolerance: the tablets contain lactose. Tell your doctor if you cannot have lactose.
• Older age: reduced kidney function is more common in older people, so kidney tests matter and doses are chosen with care.
• Pregnancy and breastfeeding: talk to your doctor about your treatment, and do not stop it on your own.

• Adults, HIV-1 or chronic hepatitis B: the US prescribing information describes one 300 mg tablet once a day, taken with or without food. The European product information describes one 245 mg tablet once a day, which is the same amount in different labelling.
• Children with HIV-1, 2 years and older: the dose is based on body weight, 8 mg/kg once a day, up to a maximum of 300 mg a day. Children who can swallow tablets and weigh at least 17 kg use weight-based tablet strengths of 150 mg, 200 mg or 250 mg.
• Children with chronic hepatitis B, 12 years and older: one 300 mg tablet once a day.
• Reduced kidney function: if your kidneys are not working well, your doctor will give the medicine less often or on a different schedule.
• Never take more than one dose in 24 hours unless your doctor has told you otherwise.
• Follow the dose and the schedule your doctor prescribes. Do not change the dose yourself.

• Experience with doses higher than the usual one is limited. In one study, 600 mg a day was given for 28 days with no serious reactions reported.
• If an overdose happens, the person is monitored for signs of toxicity and given supportive treatment in hospital.
• Tenofovir is removed by dialysis. During a four-hour session the dialysis machine clears about half the medicine from the blood (an extraction coefficient of about 54%), and roughly 10% of a single 300 mg dose is removed.
• If you think you or someone else has taken too much, contact a doctor or go to the nearest hospital straight away, and take the medicine pack with you.
• Do not wait for symptoms to appear before getting help.

• Take the missed dose as soon as you remember.
• If the next dose is almost due, skip the missed dose and take the next one at your usual time.
• Never take two doses at the same time to make up for a missed one.
• Missing doses can let the virus become resistant, so try not to miss any. If you often forget, set a daily alarm or ask your pharmacist for other ways to remember.

Get medical help straight away if you have:

• Fast, deep breathing, feeling very drowsy, or feeling sick with stomach pain (possible lactic acidosis)
• Yellowing of the skin or eyes, dark urine, pale stools, or pain in the upper right side of the tummy
• Passing much more urine than usual, being very thirsty, or swelling of the feet and ankles
• Ongoing or worsening bone pain
• Severe stomach pain that spreads to the back, with vomiting
• Muscle pain or weakness, or dark, cola-coloured urine
• A fast or irregular heartbeat, or trouble breathing
• Fever, chills or feeling generally unwell together with any of the signs above
• New or worsening symptoms after stopping treatment, especially if you have hepatitis B
• New infections or symptoms that appear months after starting treatment (possible immune reconstitution syndrome)